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This Article Full Text Full Text (PDF) Supplemental Material All Versions of this Article: 294/6/F1422    most recent 00030.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sala-Rabanal, M. Articles by Wright, E. M. PubMed PubMed Citation Articles by Sala-Rabanal, M. Articles by Wright, E. M.

Molecular mechanism of dipeptide and drug transport by the human renal H⁺/oligopeptide cotransporter hPEPT2

Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California

Submitted 21 January 2008 ; accepted in final form 25 March 2008

The human proton/oligopeptide cotransporters hPEPT1 and hPEPT2 have been targeted to enhance the bioavailability of drugs and prodrugs. Previously, we established the mechanisms of drug transport by hPEPT1. Here, we extend these studies to hPEPT2. Major variants hPEPT2*1 and hPEPT2*2 were expressed in Xenopus oocytes, and each was examined using radiotracer uptake and electrophysiological methods. Glycylsarcosine (Gly-Sar); the β-lactam antibiotics ampicillin, amoxicillin, cephalexin, and cefadroxil; and the anti-neoplastics -aminolevulinic acid (-ALA) and bestatin induced inward currents, indicating that they are transported. Variations in transport rate were due to differences in affinity and in turnover rate: for example, cefadroxil was transported with higher apparent affinity but at a lower maximum velocity than Gly-Sar. Transport rates were highest at pH 5 and decreased significantly as the external pH was increased. Our results strongly suggest that the protein does not operate as a cotransporter in tissues where there is little or no pH gradient, such as choroid plexus, lung, or mammary gland. In the absence of substrates, rapid voltage jumps produced hPEPT2 capacitive currents at pH 7. These transients were significantly reduced at pH 5 but recovered on addition of substrates. The seven-state ordered kinetic model previously proposed for hPEPT1 accounts for the steady-state kinetics of neutral drug and dipeptide transport by hPEPT2. The model also explains the capacitive transients, the striking difference in pre-steady-state behavior between hPEPT2 and hPEPT1, and differences in turnover numbers for Gly-Sar and cefadroxil. No functional differences were found between the common variants hPEPT2*1 and hPEPT2*2.

hPEPT2 substrates and drugs; kinetic model of H⁺/oligopeptide cotransport; polymorphisms